Apparatus for the extension and retraction of a peripheral device

Abstract

The present invention provides an extendible support mechanism in which a counterbalance system allows extension and retraction of the arm to be carried out with the same level of mechanical effort. Embodiments of the present invention allow the system to be used in a plurality of orientations, and thus the invention has particular utility in the extension and retraction of peripheral devices for radiotherapy systems, where use of a rotatable gantry is common.

1. An apparatus for supporting a device, comprising:
 a mount; 
 a scissors-type extension arm comprising, at a first end, a first contact point positionally fixed but pivotally connected to the mount and a second contact point pivotally and slidably connected to the mount, and, at a second end, an interface for connection to the device; and 
 a counterbalancing system having a counterweight coupled to the second contact point of the scissors-type extension arm and arranged to counterbalance the scissors-type extension arm and the device in a plurality of spatial orientations of the apparatus. 
 
     
     
       2. The apparatus according to  claim 1 , wherein the second contact point is slidable in two, opposing directions, corresponding to extension and retraction of the scissors type extension arm, and wherein the counterbalancing system is arranged to counterbalance movement of the second contact point in either direction. 
     
     
       3. The apparatus according to  claim 1 , wherein the counterweight is coupled to the second contact point as from a plurality of directions. 
     
     
       4. The apparatus according to  claim 1 , wherein the device is a portal imager for a radiotherapy system. 
     
     
       5. An imaging apparatus for a radiotherapy system, comprising:
 a mount, for fixing to the radiotherapy system; 
 an imaging device; 
 an arm coupling the imaging device to the mount, the arm and imaging device having a combined centre of gravity, the arm being capable of extension, resulting in movement of the centre of gravity in a first direction, and retraction, resulting in movement of the centre of gravity in a second, opposite direction; and 
 a counterweight, coupled to the arm so as to move in a direction opposing the movement of the centre of gravity when the arm is extended or retracted. 
 
     
     
       6. The imaging apparatus of  claim 5 , wherein the arm is a scissor-type extension arm. 
     
     
       7. The imaging apparatus of  claim 5 , wherein the arm comprises a pair of cross-members pivotally linked to each other at their respective mid-points. 
     
     
       8. The imaging apparatus according to  claim 7 , wherein the arm comprises at least one further pair of cross-members pivotally linked to each other at their respective mid-points, the at least one further pair being pivotally coupled to the pair of cross members at their respective ends. 
     
     
       9. The imaging apparatus according to  claim 5 , wherein the imaging apparatus is a portal imaging apparatus. 
     
     
       10. A peripheral apparatus for a radiotherapy system, comprising:
 a mount, for fixing to the radiotherapy system; 
 a peripheral device; 
 an arm coupling the peripheral device to the mount, the arm and peripheral device having a combined centre of gravity, the arm being capable of extension, resulting in movement of the centre of gravity in a first direction, and retraction, resulting in movement of the centre of gravity in a second, opposite direction; and 
 a counterweight, coupled to the arm so as to move in a direction opposing the movement of the centre of gravity when the arm is extended or retracted.